Intravenous liquid flow regulator

ABSTRACT

An I.V. bag is connected to a drip chamber, then to a conventional tube clamp and a regulating tube containing a wick or other material that breaks surface tension of the liquid in the tube, which flows into a bubble separator that forces any remaining entrained air through one or more hydrophobic gas permeable membranes, and then into the patient. A downstream check valve adjacent to the bubble separator prevents back flow into or through the bubble separator. An upstream check valve adjacent to the bubble separator prevents air from being drawn into the bubble separator through its gas permeable hydrophobic membrane. A vent placed adjacent to the tube clamp isolates any pressure drop above the vent, allowing a pressure head to develop in the regulating tube, which insures a constant flow of I.V. liquid into the patient regardless of downstream or upstream hydraulic conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.08/974,110, filed Nov. 11, 1997 now pending U.S. Pat. No. 6,013,060.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to an apparatus and process forregulating the rate that liquid flows through an intravenous (I.V.) setused to infuse liquids and drugs into humans and animals. Moreparticularly, the present invention is directed to an I.V. liquid flowregulator that uses a wick and a vertical tube clamp to regulate therate of flow.

2. Description of Related Art Including Information Disclosed Under 37C.F.R. Sections 1.97-1.99.

Regulating the rate of flow through an I.V. set into a patient toachieve a desired or necessary rate of infusion of liquid or dissolveddrugs is sometimes critical to successful patient treatment.Conventional I.V. sets alone do not regulate the rate of flow of liquidthrough them and into the patient. In these, after an initial air purgeand set up, the operator adjusts the tube clamp to give the desireliquid flow setting. The conventional tube clamp is in effect a simplevariable orifice device that roughly regulates the flow of liquid bysqueezing the tube more or less tightly. Therefore, changes in eitherthe upstream or downstream hydraulic conditions (as gauged from the tubeclamp) will cause changes in the flow rate across the orifice. Theupstream fluid head will gradually change as the fluid height in theI.V. bag or container slowly decreases. Because of the size of thecontainer, however, and the relatively low flow rate, the change of flowrate due to the change of column height in the I.V. bag or container isslow and predictable. The change in flow rate below the tube clamp,however, has the largest unpredictable effect on the flow rate. Patientmovement, such as rolling over, lifting an arm, standing, walking,sitting up and the like can cause significant changes in the patient'sblood pressure, which substantially changes the rate at which the liquidwill be infused into him. Further, by moving, the patient can clamp, orunclasp the vein that the catheter enters, changing the back pressure onthe liquid in the I.V. set. Any movement, or even change in certainpatient physiology, effectively alters the back pressure into which thecatheter discharges. Additional, movement of the patient can cause thetube running to the catheter to be pinched or unpinched, changing thelocal flow restriction of the transport tube and the local pressure ofliquid upstream of the catheter.

Changing any of these downstream conditions ultimately changes thepressure drop across the tube clamp of a common I.V. set, thus changingthe flow rate from the desired settings.

Currently a number of different infusion pumps designed to provide acertain defined rate of flow and therefore infusion through an I.V. setare in use. The majority of these pumps use a roller pump designed towork against the plastic tubing of the I.V. set. Although these deviceswork well, they are quite expensive and can serve only one patient at atime.

Therefore, a demand exists for an I.V. liquid flow regulator that issimple, reliable, easy to manufacture and relatively inexpensive to theultimate consumer.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providean I.V. liquid flow regulator that is simple in use and manufacture.

It is another object of the present invention to provide an I.V. liquidflow regulator that is reliable.

It is another object of the present invention to provide an I.V. liquidflow regulator that is inexpensive to the ultimate consumer.

These and other objects of the present invention are achieved byproviding a vent directly below the conventional tube clamp. The vent isopen to the air, but includes a means for preventing contamination ofthe I.V. liquid through the vent. By venting the regulating tube, thepressure drop of the I.V. system above the vent is isolated from theregulating tube. This arrangement allows the pressure head in theregulating tube to control the rate of flow of liquid through the I.V.liquid flow regulator. A wick of predetermined size and absorptioncharacteristics inside the tube downstream of the tube clamp preventsthe formation of bubbles in the transport tube under all normalconditions and a bubble separator further downstream removes any bubblesthat may have been entrained in the system.

A bubble separator separates any bubbles from the flow of liquid throughthe I.V. set and, in two embodiments, is designed to positively separateany entrained bubbles from the I.V. liquid regardless of the orientationof the bubble separator in space.

Other objects and advantages of the present invention will becomeapparent from the following description taken in connection with theaccompanying drawings, wherein is set forth by way of illustration andexample, the preferred embodiments of the present invention and the bestmode currently known to the inventor for carrying out his invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of an intravenous liquid flow regulatoraccording to the present invention set up for use.

FIG. 2 is a schematic view of the intravenous liquid flow regulator ofFIG. 1.

FIG. 3 is a cross sectional side elevation of the regulating tube ofFIG. 1 showing use of a wick to prevent bubble formation.

FIG. 4 is a cross sectional side elevation of an alternative embodimentof the regulating tube of FIG. 1.

FIG. 5 is a cross sectional side elevation of an another alternativeembodiment of the regulating tube of FIG. 1.

FIG. 6 is a cross sectional side elevation of a venting system of FIG.1.

FIG. 7 is a front elevation of an alternative venting system for usewith the present invention of FIG. 1.

FIG. 8 is a cross sectional front elevation of the venting system ofFIG. 7 taken along lines 8—8 of FIG. 7.

FIG. 9 is a cross sectional side elevation of the venting system of FIG.7.

FIG. 10 is a top plan view of one embodiment of a bubble separatorcomponent of the intravenous liquid flow regulator according to thepresent invention.

FIG. 11 is a sectional side elevation of the bubble separator of FIG. 10taken along lines 11—11 of FIG. 10.

FIG. 12 is a top plan view of an alternative embodiment of a bubbleseparator.

FIG. 13 is a cross sectional view of the bubble separator of FIG. 12taken along lines 13—13 of FIG. 12.

FIG. 14 is a side elevation of the bubble separator of FIG. 12.

FIG. 15 is a cross section of FIG. 14 taken along lines 15—15 of FIG.14.

FIG. 16 is aside elevation of an alternative embodiment of theintravenous liquid flow regulator according to the present invention setup for use shown in FIG. 1.

FIG. 17 is a top plan view of an alternative embodiment of a bubbleseparator of with a check valve.

FIG. 18 is a side elevation of the bubble separator of FIG. 17 with acheck valve.

FIG. 19 is a cross sectional view of the bubble separator of FIG. 18taken along lines 19—19 of FIG. 18.

FIG. 20 is a cross section of FIG. 14 taken along lines 20—20 of FIG.17.

FIG. 21 is a side elevation, partially in section, of anotheralternative embodiment of a bubble separator according to the presentinvention.

FIG. 22 is an enlarged cross sectional side elevation of the bubbleseparator of FIG. 21.

FIG. 23 is a cross section taken along lines 23—23 of FIG. 22.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As required by the Patent Statutes and the case law, the preferredembodiment of the present invention and the best mode currently known tothe inventor for carrying out the invention are disclosed in detailherein. The embodiments disclosed herein, however, are merelyillustrative of the invention, which may be embodied in various forms.Therefore, specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely to provide the properbasis for the claims and as a representative basis for teaching oneskilled in the art to which the invention pertains to make and use theapparatus disclosed herein as embodied in any appropriately specific anddetailed structure.

Referring now to FIGS. 1 and 2, there is shown an intravenous liquidflow regulator 10. A stand 12 having a base 14 is set onto the floor 16or other supporting surface. The stand 12 includes a horizontal armportion 18 and an upwardly bent hook 20 on the distal end of thehorizontal arm portion 18. The stand 10, arm 18, and upwardly bent hook20 are conventionally made from a single length of rod. A conventionalI.V. bag or other container 22 is conventionally suspended from thehorizontal arm 18. A drip chamber 24, for directly or indirectlymeasuring the rate of liquid flow through the regulating tube 28 isconventionally connected to an outlet tube 25 of the I.V. bag 22 at thebottom of the I.V. bag 22 with the puncture tube in the drip chamber 24inserted into the gland 25 of the I.V. bag or container 22. A regulatingtube 28 having an internal wick 30 (see FIG. 2), or other means forreducing or eliminating the formation of bubbles in the regulating tube28. A conventional tube clamp 26 is connected to the regulating tube 28at a point below the drip chamber 24 and is used to set the desiredliquid flow rate.

The regulating tube 28 extends downwardly from the drip chamber 24 to apoint near the floor 16, which may be lower than the level at which theI.V. finally enters the patient 41. The regulating tube 28 passes into abubble separator 32, which may be clamped to a lower end of the stand 12at a point near the floor 16. The bubble separator 32 forces any gasthat may have become entrained in the liquid flowing through theregulating tube 28 into the atmosphere, insuring that no gas istransfused into the patient 41. A transport tube 34 carries the liquidfrom the bubble separator 32 to the patient 41, where the liquid isinfused through a conventional catheter or venipuncture device 47. Acheck valve 36 in the transport tube 34 prevents liquid from flowingbackward from the patient 41 into the intravenous liquid flow regulator10. The desired or normal direction of flow of liquid through theintravenous flow regulator 10 is shown by the arrows 38.

A vent 39 includes, in one embodiment, a vent tee 40 inserted into theregulating tube 28 below and adjacent to the tube clamp 26. A proximalend 42 of a vent tube 44 is connected to the tee portion of the vent tee40. A vent filter is inserted into a distal end 48 of the vent tube 44,which is attached to the horizontal arm portion 18 of the stand 12 bythe vent tube clip 50.

Now referring to FIG. 1 and to FIG. 6, the vent 39 includes a bacteriafiltering air filter 60 at its distal end. If a condition develops thatstops or nearly stops the flow of liquid out of the regulating tube 28,such as a pinched transport tube, the standing column height of liquidin the regulating tube will rise until the vent tube tee 42 fills withliquid. Then isolation of the pressure drop across the tube clamp 26 islost and liquid will flow upward into the vent tube 44 forming astanding column of liquid in the vent tube 44. This standing column willtend to rise until its height is the same as the height of the liquidlevel in the I.V. bag 22, or runs out of the end of the vent tube 44. Toprevent the latter result, in the embodiment illustrated in FIGS. 1, 6,the vent tube 44 is long enough so that its distal end 48 can be and isplaced higher than the top of the I.V. bag 22. Alternatively a gaspermeable hydrophobic membrane 62 is secured across a vent port 64, by aretaining ring 66 which is fastened to the vent housing 68 by sonicwelding, gluing, or the like, eliminating the vent tube 44 to seal thegas permeable hydrophobic membrane 62 over the vent port 64 of the venthousing 68. The gas permeable hydrophobic membrane 62 allows air to flowfreely in and out of the regulating tube 28, but prevents any liquidfrom leaking out of the vent tee 40. The wick 30 passes through achannel 67 within the vent 39 of FIGS. 7-9 that helps collect and flowany liquid protruding from the wick into the lower tube without havingthe liquid contact the membrane 62, which helps prevent the internalliquid from interfering with the air flow into and out of the bottomtube. Unrestricted air transfer from the bottom tube to the vent 39 isrequired for best performance. The portion of the regulating tube 28exiting from the bottom of the vent 39 is slightly larger than the widthand depth of the channel 67. In this embodiment, the wick 30 does notrun up past the roller of the tube clamp 26. Rather the top portion ofthe wick 30 is secured in an orifice 69 in the upper portion of the venthousing 68. The orifice 69 is sized to limit the maximum liquid flowthrough the vent 39 to maintain the liquid flow within the designlimits. In either case, once normal flow conditions are restored, theheight of the standing column of liquid in the regulating tube 28 fallsto the height required for the flow conditions and steady state liquidcontrol resumes.

The pressure drop across the tube clamp 26 is isolated from downstreampressure conditions by the vent 39. The vent 39 allows the liquid flowthrough the tube clamp 26 to flow at atmospheric pressure. A stream ofliquid 43 (FIG. 2) runs down the interior side wall 52 of the transporttube 28 until it reaches the standing column of liquid 54 in theregulating tube 28. The height of the standing column of liquid 54automatically fluctuates up and down until the pressure head generatedby the standing column of liquid 54 insures that the rate of exitingliquid flow from the regulating tube 28 is equal to the incoming liquidflow. It is advantageous to make the internal volume of the regulatingtube 28 as small as possible so that the accumulation effect of theregulating tube 28 is reduced. When a change in downstream flowcondition occurs, for example, when the patient 41 sits up, the heightof the standing column of liquid 54 in the regulating tube 28 mustchange to a different level to insure a steady state liquid flow ratethrough the intravenous liquid flow regulator 10 into the patient 41.The rate of change of the height of the standing column of liquid 54 isdirectly proportional to the rate of liquid flow in, minus liquid flowout, divided by the cross sectional area of the regulation tube'sinternal diameter. The smaller the cross sectional area of theregulating tube, the faster the standing column height will change, andthe quicker the intravenous liquid flow regulator 10 will come intosteady state condition. The pressure head resident in the standingcolumn of liquid 54 provides the regulating force to deliver a constantflow rate through the intravenous liquid flow regulator 10 and henceinto the patient 41.

Reducing the internal diameter of the regulating tube 28, however,disrupts the flow of liquid down the internal side wall 52 and leads todrops of liquid forming on the internal side wall 52. Once the dropsbecome large enough to bridge the internal diameter of the regulatingtube 28, they do so, trapping air below the drops. If this occursunchecked, a mixture of liquid and air slowly accumulates in theregulating tube 28, interfering with the correct liquid flow control.

To prevent drops of liquid from forming on the interior side wall 52 ofthe transport tube 28, an internal wick 30 is added to the inside of theregulating tube 28, as shown in FIG. 3. The wick 30 occupies a fractionof the internal cross sectional area of the regulating tube 28 lying ina range of one-quarter to three-quarters of the cross sectional area.,with one-third being the preferred ratio. The wick 30 breaks the surfacetension of the liquid as it flows down the internal side wall 52 of theregulating tube 28, thereby preventing large drops of liquid fromoccurring within the regulating tube 28. The wick 30 may be made of anyof a number of suitable materials that absorb and transport liquid, thatis, that allow liquid to flow through it. A preferred material for thewick 30 is medical grade cotton. Alternatively, as shown in FIG. 4, theinternal volume of the regulating tube 28 may be more or less filledwith small beads 56 made of glass or plastic and in any desired colors.The beads 56 also break the surface tension of the liquid flowingthrough the regulating tube 28, thereby reducing the likelihood thatbubbles will form in the liquid flowing through the regulating tube 28.Referring to FIG. 5, another alternative bubble reduction systemincludes making the interior surface of the regulating tube 28 slippery,such as by coating the interior surface with a slick material on theinternal side wall 52 of the regulating tube 28, which in FIG. 5 is acoating of polytetrafluoroethene 58.

Referring now to FIGS. 10, 11, a preferred embodiment of the bubbleseparator 32 includes a housing or container 70 consisting of acontainer, having a cover 72 that includes a clamp bracket 74 connectedor formed therein, which is snapped onto the I.V. stand 12 near thefloor 16 (FIG. 1), to insure that the bubble separator 32 is retained inan upright position, that is the position shown in FIGS. 1 and 11, whichis necessary to its proper operation. The clamp bracket 74 includes apair of opposed symmetrical curved semi-circular arms 76, each having adistal outwardly turned end portion 78. The clamp bracket comprises apair of opposed inwardly curved arcuate arms adapted for clamping abouta cylindrical form. When they are pushed against the I.V. stand 12, theoutwardly turned end portions 78 are wedged outwardly, expanding thedistance between the curved semi-circular arms 76 and allowing the I.V.stand 12 fit between them. Then the elastic nature of the curvedsemi-circular arms 76 snaps them closer together into a firm frictionalengagement with the I.V. stand 12, retaining the bubble separator 32 inthe desired position on the I.V. stand 12 adjacent to the floor 16.

Still referring to FIGS. 10, 11, the regulating tube 28 is inserted intoan entrance tube receiving port 80 adjacent to one edge of the cover 72.Across a diameter of the cover 72, adjacent to the edge 84 of the cover72, the transport tube 34 leading to the patient 41 is inserted into atransport tube receiving port 84, which is sealed to and connected to anextension tube 86 fixed to the adjacent interior side wall 88. Theextension tube 86 extends downwardly to a level adjacent to but somewhatabove the bottom wall 90 to insure that the transport tube 34 drawsfluid only from below the level of the liquid 92 in the bubble separator32 at all times.

Still referring to FIGS. 10, 11, a gas permeable hydrophobic membrane isseated in a seat 96 in the cover 72 about an opening 99 in the cover andis held in place by a ring membrane retainer 98. The bubble separator 32is preferably made from plastic and the different pieces, including thering membrane retainer 98 are held in place by chemical or sonicwelding.

Any bubbles that may have become entrained in the liquid flowing throughthe regulating tube 28 are removed in the bubble separator 32. No liquidcan be transported to the transport tube 34 until enough accumulates inthe container 70 to cover the lower end of the extension tube 86. Anybubbles entrained in the liquid flowing through the regulating tube 28naturally float to the upper surface of the liquid in the container 70.The pressure head from the standing column of liquid 54 is sufficientboth to force the air through the gas permeable hydrophobic membrane 94and to force liquid through the transport tube 34 and into the patient41. During normal use, the container 70 fills but the liquid cannotescape from the bubble separator 32, because it will not penetrate themembrane 94.

The embodiment of the bubble separator 32 discussed above in conjunctionwith FIGS. 10, 11 must be positioned in an upright position, that is,with the gas permeable hydrophobic membrane 94 at the highest point ofthe bubble separator 32 to insure that entrained gas will be forced outof the liquid before being transported to the patient 41. The embodimentof the bubble separator 32 illustrated in FIGS. 12-15 overcomes thisdisadvantage by providing a bubble separator 32 that will operate toremove entrained bubbles from a flow of liquid regardless of theorientation in space of the bubble separator 32. In this embodiment, thebubble separator 32 is smaller than the embodiment of FIGS. 11 and 12and may placed in the transport tube 34 nearer to the patient 41, butupstream of the check valve 36, without regard to orientation up ordown.

Referring to FIGS. 12-15 a housing 100 includes a regulating tubereceiving orifice or port 102 at a right-hand end and a transport tubereceiving orifice or port 104 at the left-hand end for sealingfrictional engagement of the respective tubes 28, 34. A substantiallycylindrical central chamber 106 having a flow deflector or baffle 108across a diameter of the central chamber 106 perpendicular to thedirection of flow through the bubble separator 32. The flow deflector108 lies along a central span from top to bottom of the chamber 106,with the top of the chamber 106 as defined herein being the upper partof FIGS. 14 and 15. The flow deflector 108 insures that no bubbles canpass directly from the entrance port 102 to the exit port 104 byblocking the direct path between them. An upper gas permeablehydrophobic membrane 110 is sealed into an upper membrane aperture 112by a ring membrane retainer 114. The membrane 110 is seated about acircumferential seat 116 formed into the top of the housing 100 and ringmembrane retainer 114 is seated and sealed on the membrane 110. A lowergas permeable hydrophobic membrane 118 is seated into a lower membranecircumferential seat 120 and covers the lower membrane aperture 122. Thelower membrane 118 is sealed into position by the lower ring membraneretainer 124. The transport tube receiving orifice or port 102 extendsinto the central chamber 106 by an amount in the range of one-fourth toone-third of the diameter of the central chamber 106, and forms an exittube extension 126, which helps prevent any air that may have beencollected on the top membrane (whichever one that may be with the bubbleseparator 32 in a particular orientation) from entering the exit port104 when the orientation of the bubble separator 32 shifts suddenly. Anyair in the bubble separator 32 will follow the walls of the bubbleseparator 32 when it is shifted to a different orientation.

Referring to FIG. 16, an alternative embodiment of the I.V. set of FIG.1 is shown, which, includes a downstream check valve 37 downstream fromthe bubble separator 32 and an upstream check valve 43, upstream of thebubble separator 32. The downstream check valve 37 is a conventionalpre-loaded diaphragm 131, which is biased a closed position bypre-tensioning across the reduced diameter internal orifice 133. Thediaphragm 131 is stretched during installation in the check valve 37 andis then allowed to rebound into a tightened position. It prevents liquidfrom flowing from the patient 41 toward the bubble separator 32.Sometimes due to emergency transportation, the care giver placed theI.V. bag 22 beside the patient 41 or sometimes below the patient. Inthese cases, there exists the possibility that the fluid pressure in thepatient 41 is higher than the pressure head from the I.V. bag 22, andthere can be reverse flow of liquid flow our of the patient 41 into theI.V. set. Likewise, the air pressure surrounding the gas permeablehydrophobic membrane 94, 110 on the bubble separator 32 could be at ahigher pressure than the fluid pressure in the separator and air couldflow back into the bubble separator 32, completely filling it. When theI.V. bag 22 is raised back to its normal position substantially higherthan the patient 41, it would be possible for air to be pushed into thefluid exit tube for the bubble separator 32, as air was also beingvented through the gas permeable hydrophobic membrane 94, 110. Thiscould cause a very dangerous condition. The downstream check valve 37prevents any reverse flow of liquid from the patient 41 into the I.V.set. Further, the downstream check valve 37 prevents any liquid fromflowing through the bubble separator 32 until the pressure in the bubbleseparator 32 is greater than the pressure required to open thepre-loaded diaphragm 131 valve. This amount of pressure can develop onlyafter all bubbles are purged from the bubble separator 32 due to thecompressibility of the gas bubbles.

Use of a simple downstream check valve 37, however, does not prevent airfrom flowing into the bubble separator 32 from outside the bubbleseparator 32 when the external air pressure is greater than the liquidpressure inside the bubble separator 32. To prevent this result, thedown stream check valve 37 includes a pre-loaded spring biased diaphragmhaving a preselected required pressure head to cause the valve 32 toopen, all the air inside the bubble separator 32 is forced out throughthe membrane 94, 110 prior the flow of any liquid. That is, thedownstream check valve 37 ensures that any air in the bubble separator32 will be purged during startup. Liquid flowing through the I.V. setmust establish a certain predetermined pressure head in order toovercome the spring loaded downstream check valve 37, and the pressurerequired to open the downstream check valve 37 is greater than thepressure required to force air through the gas permeable hydrophobicmembrane 94, 100.

The upstream check valve 43, which need not be spring loaded, preventsliquid or gas bubbles from moving upstream from the bubble separator 32,or points lower, through the regulating tube 28 toward the I.V. bag 22,a condition that could otherwise result if the ambient air pressure isgreater than the pressure in the bubble separator 32. The upstream checkvalve 43 also prevents any air from being drawn into the bubbleseparator 32 through the gas permeable hydrophobic membrane 142 bypreventing the development of any negative pressure inside the housing132.

The downstream check valve 37 and the upstream check valve 41 are placedas near to the bubble separator as practical and all three elements arelocated near the patient's 41 venipuncture port.

Sometimes the pressure head required to drive trapped air from thebubble separator 32 is greater than the liquid pressure head required totransfer I.V. liquid into the patient 41. This condition can occur withlow flow conditions and a large diameter venipuncture device, or when novenipuncture device is attached, such as during normal startup. Thebubble separator 32 would then fill with gas from any bubbles entrainedin the liquid in the regulating tube 28 and the bubble separator 32 willthen not separate bubbles from the liquid. The downstream check valve 37prevents this condition. Again, however, the spring bias toward a closedposition must be greater than the pressure head required to vent orpurge air from the system through the gas permeable hydrophobic membrane94, 110.

Referring now to FIGS. 17-20, the bubble separator 32 is shown with theupstream check valve 37 attached between the transport tube receivingorifice 104 and the transport tube 34, which transports the I.V. liquidto the patient 41. The direction of liquid flow is shown by the arrow101FIGS. 17-20 and FIGS. 21, 22.

Referring now to FIGS. 21-23, there is shown another alternativeembodiment of the bubble separator 32, denominated as the bubbleseparator 130, which includes a cylindrical housing 132 comprising anetwork of rods 134 forming the housing or cage 132, a left-hand end cap136, which is solid, and a right-hand end cap 138, which is also solid.The housing 132 is preferably made from injection molded plastic as asingle component. Each end cap 136, 138 includes a circular recess, orvoid, 140, which is included to reduce the amount of plastic required. Agas permeable hydrophobic membrane 142 is wrapped around the form formedby the rods 134, that is the cylindrical side wall 144 of the housing132. The rods 134 form a series of ports 135 that allow gas to passthrough the membrane 124. The gas permeable hydrophobic membrane 142consists of a single sheet of material whose edges are sealed withadhesive or the like after the material is wrapped around thecylindrical side wall 144. An inlet tube 146 is inserted into an inlettube receiving aperture 148 in the right-hand end cap 138 and is sealedtherein. An outlet tube 150 is inserted into an insert tube receivingaperture 153 in the left-hand end cap 136 of the housing 132. The inlettube 150 is a straight tube having an end 156 that projects into thevoid 154 of the housing 132 a distance ranging from about ⅓ to ⅔ of thedistance from the interior surface of the left-hand end cap 136 to theinterior surface of the right-hand end cap 138, with about midwaybetween the two end caps 136, 138. The inlet tube 146 similarly projectsinto the void 154 in the housing 132 and must project into the housing132 by a distance sufficient to require the end 158 of the inlet tube148 to overlap a significant portion of the portion of the outlet tube158 inside the housing 132. As shown the inlets for the inlet tube 146and the outlet tube 150 are aligned across from one another along astraight line. In this preferred embodiment, the portion of the inlettube 146 inside the housing 132 includes a downward bend 160 adjacent tothe interior surface of the right-hand end cap 138 and a second upwardbend 162 adjacent to the end 156 of the outlet tube 150, such that theportion of the inlet tube 146 that overlaps the outlet tube 150 withinthe housing 132 underlies the outlet tube 150, allowing the overlappingportions of the inlet tube 146 and the outlet tube 150 to lie adjacentto one another. These bends 160, 162 are permanently formed in the inlettube 146. In an alternative embodiment, the inlet and outlet aperturescan be offset from a straight line in an amount that permits the use ofstraight tubes for both the inlet and outlet tubes, while still allowingthe inlet tube to underlie the outlet tube. The liquid flows in thedirection of the arrow 101 and a check valve 37, as described above, isfitted onto the outlet tube 150 adjacent to the bubble separator 132,and then through the transport tube 34.

Still referring to FIGS. 21-23, it is clear that any air entrained inliquid flowing through the inlet tube 146 is isolated from the interiorof the housing 132 and that no matter how the bubble separator 132 isoriented, there is some portion of the gas permeable hydrophobicmembrane 142 that is above the end 156 of the outlet tube 150, whichensures that any bubbles that pass through the end 158 of the inlet tube146 will float to a level higher than the end 156 of the outlet tube 150and will be exposed to the gas permeable hydrophobic membrane 142. Thus,any bubbles will be forced through the gas permeable hydrophobicmembrane 142 and cannot pass through the outlet tube 150.

Air bubbles do not normally form in the regulating tube 28, as explainedabove. If, however, the regulating tube 28 is pinched or clamped at apoint above the standing column of liquid 54, bubbles may develop, eventhough the wick 30 eliminates most of these problems. It remains,however, possible, that an air bubble may become entrained in the liquidflow and flow out of the regulating tube 28, from where it couldpossibly enter the patient 41. The bubble separator discussed above isdesigned to remove any such bubbles and insure that no bubbles reach thepatient 41. Fluid velocity inside the bubble separator 32 is low orstagnate, allowing the air to float to the top of the container. In theembodiment of FIGS. 11-15, separate gas permeable hydrophobic membranesare located in at least two places on the bubble separator 32, 130 sothat no matter what the orientation in space of the bubble separator 32,130 one or more membranes will be near enough to the highest point onthe bubble separator 32, 130 to permit any entrained air to escape tothe atmosphere.

The gas permeable hydrophobic membranes used herein must be large enoughthat the largest expected volume of entrained air entering the bubbleseparator 32, 130 can be vented at the expected head pressure of theintravenous liquid flow regulator 10. The shape and size of thecontainer portion of the bubble separator must be large enough to insurethat the fluid velocity inside the container is low or stagnate so thatentrained air bubbles have time to be displaced to the top of thecontainer for venting to the atmosphere. Similarly, the liquid paththrough the container must insure that the passing liquid is retainedinside the container long enough for the air to be displaced out of theliquid stream exiting the container. The end of the exit tube inside thecontainer must always be covered with liquid during use.

The intravenous liquid flow regulator is made from surgical gradeplastic, silicon, injected molded plastic, extruded plastic, and thelike. The components are attached to one another by gluing, sonicwelding, and the like, except the tubing, which is typically frictionfitted over coupling members. The intravenous liquid flow regulator maybe provided as a disposable unit similar to currently used I.V.administration sets, or may be made for sterilization and reuse.

Different models of the intravenous liquid flow regulator providedifferent optimal flow ranges for use when different transient responserequirements. Convenient flow rate ranges are 0-10 ml/hr; 0-100 ml/hr;and 0-1,000 ml/hr.

While the present invention has been described in accordance with thepreferred embodiments thereof, the description is for illustration onlyand should not be construed as limiting the scope of the invention.Various changes and modifications may be made by those skilled in theart without departing from the spirit and scope of the invention asdefined by the following claims.

I claim:
 1. An apparatus for regulating flow through an I.V. set comprising: a. a depending regulating tube connected to an I.V. container, said regulating tube having an upper end and a lower end; b. a transport tube connected to said regulating tube for conveying I.V. liquid to a patient; and c. means for separating entrained bubbles from the flow of liquid through said I.V. set connected through said transport tube and thereby preventing the transport of gas bubbles to said patient.
 2. An apparatus for regulating the flow through an I.V. set in accordance with claim 1 wherein said bubble separating means is connected to said transport tube.
 3. An apparatus for regulating the flow through an I.V. set in accordance with claim 1 further comprising a downstream check valve in said transport tube downstream from said bubble separating means.
 4. An apparatus for regulating the flow through an I.V. set in accordance with claim 3 wherein said downstream check valve further comprises a spring-biased check valve.
 5. An apparatus for regulating the flow through an I.V. set in accordance with claim 1 further comprising an upstream check valve in said transport tube upstream from said bubble separating means.
 6. An apparatus for regulating the flow through an I.V. set in accordance with claim 1 wherein said bubble separating means further comprises a housing having an inlet tube connected thereto and an outlet tube projecting into said housing and having an end extending into said housing and at least one sealed gas permeable hydrophobic membrane covering at least one vent port in said housing.
 7. An apparatus for regulating the flow through an I.V. set in accordance with claim 6 wherein said bubble separating means further comprises a flow deflector inside said housing between said inlet tube and said outlet tube.
 8. An apparatus for regulating the flow through an I.V. set in accordance with claim 1 wherein said bubble separating means further comprises a housing with an inlet tube inserted into said housing, an outlet tube inserted into said housing, wherein said outlet tube comprises an end set inside said housing at a distance of {fraction (1/3-2/3)} of the distance from one end of said housing to another end of said housing and said inlet tube projects into said housing by an amount to allow an end of said inlet tube to overlap a portion of said outlet tube that lies inside said housing, and at least one port in said housing, said port covered by a gas permeable hydrophobic membrane fastened to said housing.
 9. An apparatus for regulating the flow through an I.V. set in accordance with claim 8 wherein said housing further comprises a cylindrical housing having a right-hand end cap and left-hand end cap connected by a network of rods forming a cage.
 10. An apparatus for regulating the flow through an I.V. set comprising: a. a depending regulating tube connected to an I.V. container, said regulating tube having an upper end and a lower end; b. a transport tube connected to said regulating tube for conveying I.V. liquid to a patient; c. means for separating entrained bubbles from the flow of liquid through said I.V. set connected through said transport tube and thereby preventing the transport of gas bubbles to said patient; and d. a downstream check valve in said transport tube downstream from said bubble separating means.
 11. An apparatus for regulating flow through an I.V. set in accordance with claim 10 wherein said downstream check valve further comprises a spring-biased check valve.
 12. An apparatus for regulating flow through an I.V. set in accordance with claim 10 further comprising an upstream check valve in said transport tube upstream from said bubble separating means.
 13. An apparatus for regulating flow through an I.V. set in accordance with claim 10 wherein said bubble separating means further comprises a housing having an inlet tube connected thereto and an outlet tube projecting into said housing and having an end extending into said housing and at least one sealed gas permeable hydrophobic membrane covering at least one vent port in said housing and a flow deflector inside said housing between said inlet tube and said outlet tube.
 14. An apparatus for regulating the flow through an I.V. set in accordance with claim 10 wherein said bubble separating means further comprises a housing with an inlet tube inserted into said housing, an outlet tube inserted into said housing, wherein said outlet tube comprises an end set inside said housing at a distance of {fraction (1/3-2/3)} of the distance from one end of said housing to another end of said housing and said inlet tube projects into said housing by an amount to allow an end of said inlet tube to overlap a portion of said outlet tube that lies inside said housing, with said overlapping portions of said inlet tube and said outlet tube lying adjacent to one another and at least one port in said housing, said port covered by a gas permeable hydrophobic membrane fastened to said housing.
 15. An apparatus for regulating the flow through an I.V. set in accordance with claim 10 further comprising an upstream check valve in said transport tube adjacent to said bubble separating means.
 16. An apparatus for regulating the flow through an I.V. set comprising: a. a depending regulating tube connected to an I.V. container, said regulating tube having an upper end and a lower end; b. a transport tube connected to said regulating tube for conveying I.V. liquid to a patient; c. means for separating entrained bubbles from the flow of liquid through said I.V. set connected through said transport tube and thereby preventing the transport of gas bubbles to said patient; d. a downstream check valve in said transport tube downstream from said bubble separating means and adjacent thereto; and e. an upstream check valve in said transport tube upstream from said bubble separating means and adjacent thereto.
 17. An apparatus for regulating the flow through an I.V. set in accordance with claim 16 wherein said bubble separating means further comprises a housing having an inlet tube connected thereto and an outlet tube projecting into said housing and having an end extending into said housing and at least one sealed gas permeable hydrophobic membrane covering at least one vent port in said housing and a flow deflector inside said housing between said inlet tube and said outlet tube and said flow deflector being narrower than said housing.
 18. An apparatus for regulating the flow through an I.V. set in accordance with claim 10 wherein said bubble separating means further comprises a cylindrical housing having a left-hand end cap with an inlet tube inserted into said left-hand end cap of said housing, and a right-hand end cap having an outlet tube inserted into said right-hand end cap of said housing, wherein said outlet tube comprises an end set inside said housing at a distance of {fraction (1/3-2/3)} of the distance from one end of said housing to another end of said housing and said inlet tube projects into said housing by an amount to allow an end of said inlet tube to overlap a portion of said outlet tube that lies inside said housing, with said overlapping portions of said inlet tube and said outlet tube lying adjacent to one another and at least one port in said housing, said port covered by a gas permeable hydrophobic membrane fastened to said housing.
 19. An apparatus for regulating the flow through an I.V. set in accordance with claim 18 wherein said inlet tube further comprises a downward bend adjacent to said right-hand end cap and an upward bend adjacent to said end of said outlet tube.
 20. An apparatus for regulating the flow through an I.V. set in accordance with claim 19 wherein said housing further comprises a cylindrical housing having a side wall comprising a network of rods, with said gas permeable hydrophobic membrane covering said network or rods. 